--> Abstract: Application of Chemostratigraphy in the Alpine Field, North Slope, Alaska, by Steve R. Moothart, Jeffery W. Yeaton, and Ken Ratcliffe; #90039 (2005)

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Application of Chemostratigraphy in the Alpine Field, North Slope, Alaska

Steve R. Moothart1, Jeffery W. Yeaton1, and Ken Ratcliffe2
1 ConocoPhillips Alaska, Anchorage, AK
2 Chemostrat Ltd, Llanfyllin, United Kingdom

The Late Jurassic Alpine Sandstone within the Alpine Field is divided into three informal lithostratigraphic units: Alpine A, B and C. These units represent a regressive-transgressive sequence of vf-fine grained, compositionally mature, shallow marine sandstones and silty claystones. Alpine A and B sandstones are separated from the overlying Alpine C reservoir by a sub-regional lowstand erosion surface (upper Jurassic unconformity). To date, the primary reservoir objective has been the Alpine C, which infills incised paleotopography on this surface. Field development has been carried out entirely with horizontal wells evaluated with LWD. Stratigraphic complexity associated with relief on the upper Jurassic unconformity makes determination of wellbore position relative to the internal lithostratigraphy enigmatic. Future development will target the Alpine A and B units below the unconformity, highlighting the need for another tool to help distinguish the Alpine A/B units from the Alpine C unit.

Initially, a chemostratigraphic pilot study was performed on cores from vertical delineation wells in order to determine the validity and resolution of the technique. This study indicated that chemostratigraphy can geochemically distinguish the Alpine A and B units from the overlying Alpine C unit.

Subsequent to the pilot study, chemostratigraphy was carried out on cuttings samples from non-cored wells, including two horizontal development wells. From this analysis it was possible to confirm the relationship of the horizontal wellpaths to the lithostratigraphic units. As a result, this work has led to the successful implementation of an evaluation program for testing the productivity of the lower Alpine A unit.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005